fmt_helper.h

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// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
#pragma once
 
#include <chrono>
#include <type_traits>
#include <iterator>
#include <spdlog/fmt/fmt.h>
#include <spdlog/common.h>
 
#ifdef SPDLOG_USE_STD_FORMAT
#include <charconv>
#include <limits>
#endif
 
// Some fmt helpers to efficiently format and pad ints and strings
namespace spdlog
{
    namespace details
    {
        namespace fmt_helper
        {
 
            inline void append_string_view(spdlog::string_view_t view, memory_buf_t& dest)
            {
                auto* buf_ptr = view.data();
                dest.append(buf_ptr, buf_ptr + view.size());
            }
 
#ifdef SPDLOG_USE_STD_FORMAT
            template <typename T>
            inline void append_int(T n, memory_buf_t& dest)
            {
                // Buffer should be large enough to hold all digits (digits10 + 1) and a sign
                SPDLOG_CONSTEXPR const auto BUF_SIZE = std::numeric_limits<T>::digits10 + 2;
                char                        buf[BUF_SIZE];
 
                auto [ptr, ec] = std::to_chars(buf, buf + BUF_SIZE, n, 10);
                if (ec == std::errc())
                {
                    dest.append(buf, ptr);
                }
                else
                {
                    throw_spdlog_ex("Failed to format int", static_cast<int>(ec));
                }
            }
#else
            template <typename T>
            inline void append_int(T n, memory_buf_t& dest)
            {
                fmt::format_int i(n);
                dest.append(i.data(), i.data() + i.size());
            }
#endif
 
            template <typename T>
            SPDLOG_CONSTEXPR_FUNC unsigned int count_digits_fallback(T n)
            {
                // taken from fmt: https://github.com/fmtlib/fmt/blob/8.0.1/include/fmt/format.h#L899-L912
                unsigned int count = 1;
                for (;;)
                {
                    // Integer division is slow so do it for a group of four digits instead
                    // of for every digit. The idea comes from the talk by Alexandrescu
                    // "Three Optimization Tips for C++". See speed-test for a comparison.
                    if (n < 10)
                        return count;
                    if (n < 100)
                        return count + 1;
                    if (n < 1000)
                        return count + 2;
                    if (n < 10000)
                        return count + 3;
                    n /= 10000u;
                    count += 4;
                }
            }
 
            template <typename T>
            inline unsigned int count_digits(T n)
            {
                using count_type = typename std::conditional<(sizeof(T) > sizeof(uint32_t)), uint64_t, uint32_t>::type;
#ifdef SPDLOG_USE_STD_FORMAT
                return count_digits_fallback(static_cast<count_type>(n));
#else
                return static_cast<unsigned int>(fmt::
// fmt 7.0.0 renamed the internal namespace to detail.
// See: https://github.com/fmtlib/fmt/issues/1538
#if FMT_VERSION < 70000
                                                     internal
#else
                                                     detail
#endif
                                                 ::count_digits(static_cast<count_type>(n)));
#endif
            }
 
            inline void pad2(int n, memory_buf_t& dest)
            {
                if (n >= 0 && n < 100) // 0-99
                {
                    dest.push_back(static_cast<char>('0' + n / 10));
                    dest.push_back(static_cast<char>('0' + n % 10));
                }
                else // unlikely, but just in case, let fmt deal with it
                {
                    fmt_lib::format_to(std::back_inserter(dest), SPDLOG_FMT_STRING("{:02}"), n);
                }
            }
 
            template <typename T>
            inline void pad_uint(T n, unsigned int width, memory_buf_t& dest)
            {
                static_assert(std::is_unsigned<T>::value, "pad_uint must get unsigned T");
                for (auto digits = count_digits(n); digits < width; digits++)
                {
                    dest.push_back('0');
                }
                append_int(n, dest);
            }
 
            template <typename T>
            inline void pad3(T n, memory_buf_t& dest)
            {
                static_assert(std::is_unsigned<T>::value, "pad3 must get unsigned T");
                if (n < 1000)
                {
                    dest.push_back(static_cast<char>(n / 100 + '0'));
                    n = n % 100;
                    dest.push_back(static_cast<char>((n / 10) + '0'));
                    dest.push_back(static_cast<char>((n % 10) + '0'));
                }
                else
                {
                    append_int(n, dest);
                }
            }
 
            template <typename T>
            inline void pad6(T n, memory_buf_t& dest)
            {
                pad_uint(n, 6, dest);
            }
 
            template <typename T>
            inline void pad9(T n, memory_buf_t& dest)
            {
                pad_uint(n, 9, dest);
            }
 
            // return fraction of a second of the given time_point.
            // e.g.
            // fraction<std::milliseconds>(tp) -> will return the millis part of the second
            template <typename ToDuration>
            inline ToDuration time_fraction(log_clock::time_point tp)
            {
                using std::chrono::duration_cast;
                using std::chrono::seconds;
                auto duration = tp.time_since_epoch();
                auto secs     = duration_cast<seconds>(duration);
                return duration_cast<ToDuration>(duration) - duration_cast<ToDuration>(secs);
            }
 
        } // namespace fmt_helper
    } // namespace details
} // namespace spdlog